(a) Field of the Invention
The present invention relates to a fuel cell vehicle, more particularly, to a cooling unit of an air compressor applied to a fuel cell system of a fuel cell vehicle.
(b) Description of the Related Art
In general, a fuel cell vehicle is provided with a fuel cell system that is a power supply for driving a driving motor to generate electrical energy by an electrochemical reaction between hydrogen and air by a fuel cell.
The fuel cell system includes a stack in which fuel cells are stacked, a hydrogen supply system which supplies hydrogen to the stack, an air supply system which supplies air to the stack, and a cooling system which cools heat generated from the stack.
In particular, the air supply system includes an air compressor which compresses air and supplies the compressed air to the stack, and a humidifier which humidifies the compressed air using moisture generated at the stack.
However, a temperature of the air compressed by the air compressor under a high power operational condition of the stack is raised to about 100 to 150° C. due to a high compression ratio and a large amount of air.
The temperature of the compressed air is higher than 60 to 80° C., which is a normal operational temperature of the stack, and thus acts as a disadvantageous condition to humidification efficiency of the humidifier and operational efficiency of the stack. Therefore, it is necessary for the fuel cell system to cool the high-temperature compressed air that is supplied to the humidifier by the air compressor.
In addition, it is very important to cool a motor rotating an impeller and a bearing that supports a rotation shaft of the motor for determination of performance and life-span of an entire device in a turbo-type air compressor that rotates with high-speed.
In case of the motor, a coil may be damaged or an insulation problem may occur if heat generated from a coil wire or a magnet of a rotor is not sufficiently cooled. In addition, a rare-earth-based magnet used in the motor may be weakened due to heat, and therefore the magnet also needs to be cooled.
Further, the motor of the air compressor needs a bearing for supporting the rotation shaft, and a reasonable temperature is set according to the type or a material of the bearing, and accordingly, the bearing also needs to be sufficiently cooled.
In general, the bearing and the motor are cooled by utilizing air at an outlet of the air compressor. In this case, the air at the outlet side has already been compressed with high temperature so that the bearing and the motor cannot be sufficiently cooled.
In particular, air at the outlet of the impeller is flown into the motor through a rear side of the impeller, and the air cools the bearing at the front side by flowing through an internal path and then sequentially cools the motor and the bearing at the rear side. After that, the air is exhausted to the rear side of circulated in the motor and then returned to an entrance of the impeller.
In this case, the air at the outlet side of the compressor is increased, although it may be different according to specifications of the compressor, over 100° C. when an outlet pressure exceeds 2 bar. In particular, in case of a grease-impregnated ball bearing in which an oil lubrication and cooling structure is not included, a reasonable temperature should not exceed 150° C. Thus, in a conventional art, a temperature of a cooling air is too high to cool the bearings and the motor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.